1. Field of the Invention
The present invention relates to threaded fasteners and, more particularly, to flange nuts used as mixing delay devices in mine roof bolt installations.
2. Description of the Prior Art
Mine roof bolts, bearing plates, and resin/catalyst cartridges are often used in mine roof support systems. In a general installation, the resin/catalyst cartridge is inserted into the bore hole, followed by a first end of the mine roof bolt. A second externally-threaded end of the mine roof bolt is generally positioned through an orifice defined by the mine roof plate. In tensionable mine roof bolts, a threaded nut is usually received on the second externally-threaded end of the mine roof bolt.
The mine roof bolt is then rotated, causing the resin/catalyst to mix and ultimately cure. If the threaded nut is permitted to advance toward the first end of the mine roof bolt during mixing, the mine roof bolt will not rotate properly, and the resin/catalyst will not mix. Therefore, it is advantageous to delay the advancement of the threaded nut until the resin has cured. Once cured, the resin prevents further rotation of the mine roof bolt, and the threaded nut may then be advanced toward the first end of the mine roof bolt, securely holding the bearing plate in place and allowing the cable bolt to be tensioned.
There are multiple prior art methods and structures which have sought to initially fix a threaded or non-threaded nut during rotation of the mine roof bolt. These methods include the use of delay mechanisms, such as shear pins or plaster thread inserts, as well as various nut thread arrangements.
For example, U.S. Pat. No. 3,979,918 to Vidler teaches deformations positioned adjacent to one end of an inner threading of a nut. These deformations allow the nut to cease rotating with respect to the mine roof bolt when the area of the deformations is reached. Continued rotation of the nut after the deformations are reached causes the entire mine roof bolt to rotate, mixing the resin/catalyst. Once the resin/catalyst hardens, continued rotation of the nut causes the mine roof bolt to defeat the deformations, allowing the nut to advance along a length of the mine roof bolt.
U.S. Pat. No. 5,282,698 to Wright et al. discloses a threaded fastener or nut with longitudinally-extending, V-shaped notches at an end of the nut. When the resin/catalyst has hardened and a mine roof bolt ceases to rotate, continued rotation of the nut pushes the V-shaped notches away from the mine roof bolt, allowing the nut to be further tightened.
U.S. Pat. No. 5,417,520 to Rastall discloses an internally-threaded nut with dimples stamped on a flat portion of an end of the nut to deform the internal threads. These dimpled areas allow the mine roof bolt and internally-threaded nut to be uniformly rotated until the resin/catalyst hardens. Once the resin/catalyst hardens, the dimples yield to the mine roof bolt, allowing the threaded nut to advance along a length of the mine roof bolt.
Finally, U.S. Pat. No. 5,954,456 to Bowles discloses an internally-threaded nut having an outwardly-extending end portion, which is coined to reduce the pitch of the threads at an end of the nut. As with the previously-discussed patents, this reduction in thread pitch near the end of the internally-threaded nut allows the internally-threaded nut to be rotated relative to the bolt until these lower-pitched threads are reached. After the lower-pitched threads are reached, the internally-threaded nut and mine roof bolt rotate together until the resin/catalyst hardens. At this point, further torque on the internally-threaded nut forces the nut along a length of the mine roof bolt, allowing the internally-threaded nut to be torqued.
There are several drawbacks of the prior art nut elements. Expensive tooling costs can be involved in pitch reduction, dimpling, creation of a dome structure, or creating other hard-to-machine deformations or indentations. It is also often necessary to control, within acceptable limits, the breakout torque for the nut, and the prior art methods have limitations on the breakout torque. Hence, a need remains for an improved flange nut which is easy to manufacture, has reduced machining costs, and can meet varying breakout requirements for the nut.
The present invention seeks to obviate the disadvantages of the prior art by providing a nut having a nut body, a first end, a second end, and defining an orifice extending between the first end and the second end. A plurality of first threads and a malformed thread are each positioned in the orifice defined byte nut body, wherein the malformed thread interrupts continuity of at least one of the plurality of first threads. More particularly, the plurality of first threads are positioned at a receiving end of the nut body in the orifice defined by the nut body. Each of the first threads have a uniform height, a uniform pitch, and form lead-in threads for the nut. The malformed thread positioned in the orifice defined by the nut body following the first threads has a thread height which is greater than or less than the uniform height of the plurality of first threads and a pitch, as measured from a neighboring one of the plurality of first threads, which is substantially equal to the uniform pitch of the first threads. The malformed thread interrupts continuity of at least one of the plurality of first threads for temporarily preventing the nut from being advanced along the externally threaded shaft, wherein at the application of a predetermined torque on the nut the malformed thread is tapped by the external threads of the shaft.
The nut body further defines an interior nut wall. The malformed thread may be an untapped portion of the interior nut wall, a partially tapped thread, a thread which has been stripped, or any thread having a thread height which is larger than a thread height of any one of the plurality of first threads.
In general, one method of producing a nut according to the present invention includes the steps of: (a) making a nut body having a first end and a second end; (b) defining an orifice in the nut body which extends between the first end and the second end; (c) positioning a plurality of first threads in the orifice defined by the nut body; and (d) interrupting the plurality of first threads with a malformed thread. The step of interrupting the plurality of first threads with a malformed thread may be accomplished by stripping one of the plurality of uniformly-pitched first threads, partially tapping the interior nut wall, not tapping a portion of the interior nut wall, or forming a thread having a thread height greater than the thread height of any one of the plurality of first threads.
In one exemplary application, a resin mixing delay system for mine roof support is also provided. The system generally includes a mine roof bolt having a first bolt end defining a plurality of external threads and a flange nut body. The flange nut body has a first end, a second end, and defines an orifice extending between the first end and the second end. A plurality of uniformly-pitched first threads are positioned in the orifice defined by the flange nut body, with each of the plurality of uniformly-pitched threads having a substantially equal thread height. At least one malformed thread positioned in the orifice defined by the body. The malformed thread has a thread height that is greater than or less than the thread height of any one of the plurality of uniformly-pitched threads.
In this example, the plurality of uniformly-pitched first threads receives the plurality of external threads defined by the first bolt end of the mine roof bolt. The mine roof bolt has a second bolt end and may further include a mechanical anchor positioned between the first bolt end and the second bolt end. The flange nut body may further define an enlarged cavity portion adjacent to the first end of the flange nut, a square-shaped drive head, and a flange.
It is, therefore, an object of the present invention to provide an improved flange nut which is easy to manufacture and requires low manufacturing costs. It is a further object of the present invention to provide a flange nut for torque tension applications where the breakout torque is tightly controlled.
The invention, both as to its construction and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with accompanying drawings.